Paper comprising collapsed regenerated cellulose fibers



March 16, 1965 H. F. WISE ETAL 3,173,830

PAPER COMPRISING COLLAPSED REGENERA'IYEDCELLULOSE FIBERS Filed June 161959' II/II,

I III, III/II WM 0 f llll ll/l ffllllJ fimw M1 United States Patent3,173,830 PAPER COMPRISTNG (ZOLLAPSED REGEN- ERATED CELLULOSE FIBERSHarold F. Wise, .lames H. Filling, Don S. Nelson, and

John Wharton, Mobile, Ala, assignors, by mesne assignments, toCourtaulds, Limited, London, England, a

British company Filed lane 16, 195?, Ser. No. 320,6tl2 11 Claims. (Cl.162-446) This invention relates to a new type of paper and to a newpaper-making process.

Many proposals have been made over the years for introducing regeneratedcellulose fibers into paper. In general, it has been felt that ifregenerated cellulose fiber could be incorporated into paper, advantagescould be obtained because the fiber could be tailor made as to staplelength, denier and the like according to the properties desired in thepaper.

In conventional paper made from natural cellulose, i.e. wood pulp, rags,and the like, the paper is bonded by the interlocking of fibrils whichare produced when the stock is beaten. Unfortunately, regerenatedcellulose fibers cannot be fibrill'ated by beating in the same way thatnatural cellulose can be, and so with regenerated cellulose fibers, someother source of bonding has to be employed.

It has been proposed to add various adhesives to the paper stock; suchtechniques, however, add considerably to the cost of the paper. It hasalso been proposed to treat a newly laid down paper sheet with causticsoda to cause softening and coalescence of the fibers. Treatments ofthis nature are, however, not Well suited to incorporation inpaper-making processes on conventional paper-making machines.

It has now been discovered that certain types of regenerated cellulosefibers have sufiicient natural cohesion to form a strong bond withoutthe addition of any external adhesive. Such fibers are characterized bya crosssection (taken in a direction substantially perpendicular totheir axes) in which one dimension is from about five to about fifteentimes the other. Preferably, they contain between about 1.5 and about4.0% by weight of a finely divided inert particulate material. Suchfibers can be used by themselves in conventional paper-making processes,without added adhesive, to give a smooth, strong sheet.

The invention, therefore, comprises a paper containing between about 10%and 100% by weight of regenerated cellulose fiber, each of said fibershaving a crosssection in a plane perpendicular to its axis such that onedimension is from 5 to 15 times the other.

The invention further comprises in a method for making paper wherein aslurry of fibers is deposited on a surface and liquid is moved therefrom.to form a paper sheet, the improvement which comprises forming saidslurry at least in part from generated cellulose fibers having acrosssection in a plane perpendicular to its axis such that onedimension is between about 5 and about 15 times the other.

The drawing is a cross sectional view, greatly enlarged, of aregenerated cellulose fiber as used in the present invention, taken in aplane perpendicular to its axis.

The fibers which are used in the present invention are preferablycollapsed hollow fibers made by extruding a viscose containing asuitable gas-forming agent and preferably also containing an inertparticulate material, into a ice conventional spinning bath. As they areremoved from the spinning bath the fibers are of tubular shape, but uponsubsequent washing and drying, they collapse to give fiat filaments.

More specifically, filaments having the dimensions required for thepresent invention may be made by extruding a conventional viscosecontaining 1040% on the weight of the cellulose, of an alkali oralkaline earth metal carbonate or bicarbonate into an acid spin bath.Thus, for example, suitable fibers can be made by extruding a viscosecontaining 610% by Weight cellulose, 57% NaOI-i, 1-4% sodium carbonate,having a total sulfur content of say 1.5 to 3 and a salt number of 5.0to 7.0 into a spinning containing 11.5-12.5% by weight H 0.5 to 2% ZnSOand 18-25% Na SO Preferably the viscose will also contain from about0.15% to about 0.40% of an inert particulate material.

After emerging from the spinning bath, the fibers may be cut up to forma blanket of staple fibers and then subjected in the form of a blanketto the various washing treatments customarily given regeneratedcellulose fibers, such as a regenerating treatment with dilute acid, adesulfurizing treatment with Na 'S and a sou-ring treatment, again withdilute acid. Following this the blanket may be dried and stored; or itmay be sent directly to a papermaking plant, where it can be opened byjets of water to form a suitably slurry.

Instead of being treated as a blanket of cut staple, the fibers may betreatedin the form of a tow with the various washes'outlined above; andcut up into staple at some later time.

Thus, the fiber on coming from the spinning bath may be laid down as atow in a plaited pattern on a moving belt, and subjected to the variouswashes in that form. After treatment the tow may be dried and stored. Itmay be furnished to the paper-making plant as tow; or it may be cut upinto staple fiber beforehand.

The fiber as used preferably has a denier of about 1.5 to about 8 and isfrom say A3" to 1 /2", preferably from A" to ,42 long.

In the drawing a fiber of the type used in the invention is seen incross section. It will be observed that its width, i.e. the dimension1:, is from 5 to 15 times its thickness, i.e. the dimension a.

The inert particulate material used in the present invention may bevirtually any solid material which is inert with respect to the viscoseand the spinning bath. Titanium dioxide is preferred, but alumina,silica, carbon black, and various pigments may also be used. The role ofthe inert material is twofold. In the first place it aids in formingfibers which are evenly inflated or tubular along their length byproviding nuclei for the formation of gas bubbles. Thisfunction of thesolid particles has been used hitherto in making inflated fibers.However, were the solid used only as an aid in gas formation, a muchsmaller amount, say 0.1% on the weight of cellulose, would besulficient. The second function of the solid material is to raise fiberto fiber friction. The means by which this is accomplished is not known,but at least 1% on the weight of cellulose appears to be necessary foran appreciable effect to be obtained. There is no great advantage inusing more than about 4%. The average particle size of the materialshould be not greater than about 1 micron and, preferably, particlesabove 5 microns in size should be absent.

Paper according to the present invention may consist wholly ofregenerated cellulose fibers or it may consist partly of regeneratedcellulose fibers and partly of conventional natural cellulose fibers,e.g. paper pulp.

Besides simple blends of the special regenerated cellulose fibersreferred to above with conventional cellulose fibers, other materials,cellulosic and non-eellulosic, may be used in papers according to theinvention. Thus, for example, the invention includes blends of thespecial regenerated cellulose fibers with nylons, acrylic fibers,polyester fibers; cellulose acetate and other cellulose organic esterfibers. Such blends may or may not include conventional cellulosepaper-making fibers. Normally at least regenerated cellulose fibersarerequired toappreciably affect the characteristics of the finalproduct.

In making paper according to the invention, the regenerated cellulosestaple fiber need not be subjected to the prolonged beating that isrequired forconventional, natural paper-making fibers, since thecohesion of the novel paper does not depend on fibrillation, which isone of the more important effects of beating conventional fibers. It isdesirable, however, to create an even slurry of the fibers for use inpaper-making machines and one way to achieve this effect is to run thefibers through a refiner or Jordan engine, as a slurry containing fromsay .1 to 5.0% by weight fibers. Other mixing devices may be used; forexample, in making hand sheets for test purposes, a Waring Blendor and aTappi Standard Disintegrator have both been used successfully.

In many instances blends of the regenerated cellulose fiber andconventional paper-making fibers are desirable. In preparing suchblends, the conventional fibers may be beaten in a beater to the desiredfreeness (say 500 Canadian) and then the regenerated cellulose componentadded. After circulating through the beater just enough to disperselarge concentrations of regenerated cellulose fiber, the mixture may besent to a Jordan for further mixing and for further refining of thenatural paper. The fiber concentration in the beater (after addition ofregenerated cellulose) is about 1.0 to 6.0%. In the Jordan it is aboutone-half that.

When the fiber has been dispersed as a slurry, it is formed into a paperby any conventional method. In the laboratory, test sheets are made froma slurry having 'a fiber concentration of say 0.05 to 0.2% on a StandardBritish Sheet Mold. Usually, following Tappi Standard T205 M-53, aconcentration of 0.15% is used. For

large scale production, any conventional machine of the Fourdrinier typemay be used. In such machines an aqueous slurry containing say 0.1 to1.0% fiber is formed in the head box of the machine and is then pouredonto a moving screen where the water is sucked off to form the paper.The paper may be pressed and dried as desired in accordance withconventional practice.

If desired, conventional sizes may be added to the fiber at any stage inthe process, from the beater to the head box of the, paper-makingmachine. Alternatively, sizes may be applied to the paper after it hasbeen formed. The character and quantity of the size depends on the useto which the paper is to be put, as will be understood by those skilledin the art.

Paper made according to the invention is in general less dense and moreporous than comparable paper made from paper pulp. It has, in general,lower tensile strength but greater tear strength, greater fold strengthand greater bursting strength than similar papers made from wood pulp.

The invention will be further described with reference to the followingspecific examples which, it will be understood, are given (for purposesof illustration only and are not to be taken as in any way restrictingthe invention beyond the scope of the appended claims.

EXAMPLE I A viscose is prepared having the following characteristics:

Cellulose percent by weight 7.5

NaOH do 6.0 Na CO do 2.5 Total sulfur do 2.1 Salt index do 5.0

This is spun into a spinning bath having a temperature of about 48 C.and the following composition (Wt. )1

H 12.0 335 21%? 3. 4 Water balance -at room temperature with a finalneutral rinse at 70 C.

The blanket is then dried and stored.

Upon examination it is found that the individual fibers are fiat,deflated tubes each having a cross-section in a plane perpendicular toits axis such that on the average one dimension is about ten times theother.

The fibers made as above are used to make paper test sheets 6%" indiameter on a British Standard Sheet Mold. Four different types ofsheets are made up. In trial A the sheets are made solely from pinepaper pulp (500 freeness). In trial B the sheets contain 75% by weightpine paper pulp (500 freeness) and 25% of the regenerated cellulosefiber. In trial C the sheets consist of 50% regenerated cellulose fiberand 50% pine paper pulp (500 freeness). In trial D the sheets areregenerated cellulose.

In making the sheets the regenerated cellulose fiber is opened by jetsof water to form a slurry. This slurry is then put into a standard Tappidisintegrator with conventional pulp as appropriate and sufiicient waterto bring the fiber concentration to about 1.75% by weight. Thedisintegrator is run for 300 counts to form a smooth dispersion. Thisdispersion is diluted to 0.15% by weight and the sheets are made on aStandard British Sheet Mold. They are given a first pressing of 50p.s.i. for five minutes. They are then reversed on a dry blotter andrepressed at 50 p.s.i. for two minutes. Finally, they are dried at 50%relative humidity and 23 C. (73 F.) until equilibrium is reached withthe conditioning atmosphere. This procedure is in accordance with TappiStandard T220 M-53. The sheets are then tested for tear factor, porosity(air), tensile strength, breaking length, stretch and fold strength. Theresults appear in Table I below:

Table I Sample A B C D Percent Rayon (by weight) 0 25 50 100 PercentPulp (by weight) 100 75 5O 0 Basis Weight Oven Dry (Weight; in

pounds of 500 sheets 24 x 40") 43.0 42.6 42. 1 44. 5 Caliper (Thicknessin inches x 0.001) 3. 7 3. 8 4.0 5. 4 Apparent Density (Basis Weight/Caliper 11.6 11.2 10.5 8. 2 Tear Factor 123 142 189 265 Air Porosity(see/100 cc.) 19 9 4 0 Tensile Strength (lbs/0.5" width) 14. 3 12. 2 9.5 4. 7 Breaking Length (meters) 7, 270 5, 700 2, 680 Stretch (percent)3.1 3.7 3. 7 1. 4 Fold (MIT) 909 714 706 644 Details of the tear factortest are found in Tappi Stand-' EXAMPLE II Example I is repeated exceptthat the tow emerging from the spinning bath is subjected to the washtreat ments in that form. After drying it is cut by hand into staplefibers exactly 4" long. These fibers are then used to make up two typesof test sheets using the procedure of Example I. Type A contains 25%regenerated cellulose and 75% pine paper pulp (500 freeness). Type B isa 50-50 blend of the same stocks. Test results are shown in Table II.

Table II Sample Percent Rayon (by weight) 25 50 Percent Pulp (by weight)75 50 Basis Weight Oven Dry 42. 6 40. 6 Caliper 4. 7 5. Apparent density9. 1 7. 4 Tear Factor 231 438 Air Porosity (Sec [100 cc 3 1 TensileStrength (lbs l 10.2 6. 5 Breaking Length (Ineters) 6,080 4,080 Stretch(percent) 3. 0 2. 3 Fold Strength (MIT) 548 1,047

EXAMPLE III The procedure of Example I is repeated except that theviscose has the following composition: Cellulose percent by weight 7.5NaOH do 6.0 Na CO do 25 TiO do 0.19 Total sulfur do 2.1 Salt index 6.0

The staple fibers after washing and drying are found to have across-section in which, on the average, one dimension is 12 times theother.

Hand sheets are made up as in Example I. Sheet A is 100% pine pulp (500freeness), sheet B 25% regenerated cellulose and 75% pine pulp, sheet C50% regenerated cellulose and 50% pine pulp, and sheet D 100%regenerated cellulose. The characteristics of these sheets are shown inTable III.

Table 111 Sample A B o D Percent Rayon (by weight) 0 25 50 100 PercentPulp (1) weight) 100 75 50 0 Basis Wei ht Oven Dr 40.8 42.1 17.0 14.3Caliper 3. 9 4. 2 4. 6 4. 3 Apparent Dens 10.5 10.1 10.4 10.4 TearFactor 137 123 153 348 Air Porosity (sen/100 ee.) 11 18 18 TensileStrength (lbs./% width 12.7 11.0 10.6 0.1 Breaking length meters) 7,0207, 000 5, 620 3,473 Stretch (percent) 3.1 3.8 3.5 2. 0 Fold Strength(MIT) 403 713 685 702 EXAMPLE IV To show the difierence between fibersaccording to the invention and conventional rayon, sheets are made upwith varying proportions of normal textile grade rayon staple fiber andpine pulp. Sample A has 10% rayon, sheet B rayon and sheet C 50% rayon.Sheets made from 100% rayon are so weak that they cannot be tested. Theresults of tests on the other sheets are shown in Table IV.

Table IV Sample Percent Rayon (by weight) 1O 25 50 Percent Pulp (byweight)- 75 50 Fold Strength (MIT) 699 333 50 Mullen Bursting Strength111 87 50 Sheets made according to the process of Example I have Mullenfactors as follows:

90% pulp/10% rayon 543 75% pulp/25% rayon 560 50% pulp/50% rayon 584rayon 644 100% pulp 523 What is claimed is:

1. Paper comprising regenerated cellulose fibers, each of which has across-section in a plane perpendicular to its axis such that onedimension is between about 5 and about 15 times the other.

2. The paper claimed in claim 1 wherein the regenerated cellulose fibercomprises between about 10% and 100% of the weight of the paper.

3. Paper comprising regenerated cellulose fibers, each of said fibershaving a cross-section in a plane perpendicular to its axis such thatone dimension is between about 5 and about 15 times the other andcontaining be tween about 1.5% and about 4.0% by weight of an inertparticulate material.

4. The paper claimed in claim 3 wherein the regenerated cellulose fibercomprises between about 10% and 100% of the weight of the paper.

5. Paper comprising regenerated cellulose staple fibers, each of saidfibers being in the shape of a collapsed tube and having a cross-sectionin a plane perpendicular to its axis such that, on the average, onedimension is between about 5 and about 15 times the other.

6. Paper as claimed in claim 5 wherein the fiber contains from about1.5% to about 4.0% by weight of an inert particulate material.

7. Paper as claimed in claim 6 wherein the inert particulate material istitanium dioxide.

8. Paper comprising wood pulp and not less than 10% by weightregenerated cellulose fibers, each of said rcgenerated cellulose fibershaving across section in a plane perpendicular to its axis such that onedimension of said cross-section is fi'om 5 to 15 times the other.

9. Paper containing as its sole fibrous component, regenerated cellulosefibers each of which is characterized in having a width from 5 to 15times its thickness and in containing from about 1.5% to about 4.0% byweight titanium dioxide.

10. Paper comprising regenerated cellulose fibers wherein a predominateportion of said fibers is composed of fibers, each of which has across-section in a plane perpendicular to its axis such that onedimension is between about 5 and about 15 times the other.

11. Paper comprising regenerated cellulose fibers which have a ratio ofwidth to thickness of from about 5:1 to about 15 :1.

References Cited by the Examiner UNITED STATES PATENTS 1,464,048 8/23Rousset 28-82 2,798,283 7/57 Magat et a1. 2882 FOREIGN PATENTS 674,5776/52 Great Britain. 687,041- 2/53 Great Britain.

DONALL H. SYLVESTER, Primary Examiner.

RICHARD D. NEVIUS, JOSEPH B. SPENCER,

MORRIS O. WOLK, Examiners.

11. PAPER COMPRISING REGENERATED CELLULOSE FIBERS WHICH HAVE A RATIO OFWIDTH TO THICKNESS OF FROM ABOUT 5:1 TO ABOUT 15:1.